Gas fireplaces generally include a casing for containing the fire, a firebox mounted within the casing in a manner which permits air from inside a dwelling to circulate thereabout and be warmed, a gas burner for connection to a gas supply, and an arrangement of simulated solid fuel material located relative to the burner in a manner which gives an aesthetically pleasing natural fire appearance when in use. The casing and firebox are provided with an opening and a window respectively, by which means persons may view the fire. In some instances the simulated solid fuel is arranged to have the appearance of a coal fire, or bed of coals. In North America simulated wood log fires predominate.
The nature of simulated fire displays is such that it may be advantageous to locate the simulated logs in a generally rearwardly ascending display such that more of the fire is visible. Most commonly the simulated logs are arranged in a tier-like fashion. However the logs or coals may be arranged, it is generally desirable to produce a corresponding flame display in a manner which gives the appearance of the entire log set burning. The careful matching of burners to simulated log or simulated coal arrangements to produce aesthetically pleasing results is a science of much subtlety.
It is known to direct gas jets against simulated log or ember materials to simulate the appearance of glowing coals, and that cooler flames have a more yellow appearance similar to the appearance of a natural wood fire. However, it is also known that directing flames to impinge upon relatively cool high thermal mass ceramic or concrete logs may lead to incomplete combustion, sooting, and unacceptable pollutant emissions. One technique used to produce simulated glowing embers is to place a gas manifold in or beneath a bed of emberizing material, such as low density rock wool. Another technique is to direct flames at soft ceramic material, whose surface then glows. In either case a stable flame pattern may yield a constantly glowing body rather than a flickering effect.
The production of a glowing portion of a log, or an ember strip, or a bed of simulated glowing coals often requires the careful placement of ember simulating materials relative to flames emanating from a burner. In some instances the glowing material is loosely deposited on the burner itself, or in a tray about the burner. The glow produced may also vary on the installation of a log set on delivery, a relatively small change in the spacing between logs, or their relative angles of placement, may result in an unexpected hot or cool spot. It is advantageous to control the relative dimensions of adjacent glowing and non-glowing elements to reduce the likelihood of such unexpected results.
The problem of rearwardly ascending logs may be addressed by providing a rearwardly ascending burner, such as the two-run U-tube burner in U.S. Pat. No. 5,081,981 issued Jan. 21, 1992 to Beal. or the H-shaped welded burner of U.S. Pat. No. 5,052,370 issued Oct. 1, 1991 to Karabin. Another alternative is to employ fore and aft burners, as in U.S. Pat. No. 5,388,566 issued Feb. 14, 1995 to Smith et al.
A disadvantage of such tube run burners is that they may yield the appearance of a straight line, or curtain of flame, rather than a more random natural appearance. One attempt to give a more random effect is shown in U.S. Pat. No. 5,392,763 issued Feb. 28, 1995 to Shaw et al., in which each of a plurality of pipes having a plurality of openings follows a twisted path to a desired location. Another attempt to give a more random flame distribution is to use a pan burner with more randomly located openings, be they pinholes or slots, designed to match a less tier-like log set, such as is shown in U.S. Pat. No. 4,726,351 issued Feb. 23, 1988 to Whittaker et al., or U.S. Pat. No. 5,671,727 of Squires et al., laid open Jun. 24, 1996.
As noted above, it may be desirable to have a burner flame port in a configuration other than a pinhole. Holes formed by drilling, piercing, slitting, laser cutting and other conventional means are well known. The aspect ratio of a slot is defined as the ratio of its characteristic length to its characteristic width, whether those characteristic dimensions are the length and width of a rectangular slot, the arc length and width of a non-linear slot, or the major and minor axes of an oval or elliptical slot. The repeated heating and cooling cycles of pan burners, often with local hot and cool spots, may lead to deformation of the burner, and in particular, to deformation of the top sheet of the burner over time. An apparently minor distortion adjacent to an high aspect ratio slot may yield undesired changes in the flame patterns, and pollutants, produced. It is advantageous not only to maintain the geometric relationship of the various heated and glowing members, but also to maintain slot geometry.
It is known to provide pan burners with internal baffling, brackets, top hat sections, and even dead air-space walls. This has the disadvantage of increasing the number of parts required and the number of assembly operations, and it is generally desirable to avoid a large number of internal parts. The use of drawing and punching techniques before assembly reduces the need for extra parts, and permits local stiffening of the burner panel adjacent particular burner ports as may be desired. Notably, while a flat plate can be punched or drawn easily, it is rather more difficult to produce an outward blister or rib in a tube burner.
Although pan burners have been designed for modest angles of inclination, the design of gas manifolds to deliver combustible gas at different levels within a firebox requires some care in light of buoyancy effects. A combustible gas, such as natural gas, less dense than the surrounding ambient air will have a tendency to collect in the highest regions of the burner first, and may resist distribution to lower regions. Conversely a gas of greater density, such as propane, may pool in the lower regions of a burner, and produce an unsatisfactory flame pattern at raised locations. Restriction of port size in one area of a burner to offset buoyancy effects may also limit the ability to produce a desired appearance at that, or other locations. Such a restriction may also not be advantageous for a change to a fuel of different density, or to a different proportion of primary air.
Single inlet gas burners are well known. One disadvantage of such burners is that, by their nature, they deliver only one mix of combustion gases for all parts of the burner. The mix of gases delivered depends on the extent to which primary air is introduced into the gas stream. Typically, the amount of entrained primary air is controlled by a valve between the gas supply main and the manifold. At present the mix is uniquely determined for the entire burner by the setting of that valve. However, one may wish to use a relatively rich fuel mix in some regions of the burner, and a lean mix in others. In the one case a large, more yellow flame may result, in the other a hotter flame may be desired for heating ember materials to produce a glow.
It is known, as for example in Whittaker, above, and in U.S. Pat. No. 4,305,372 issued Dec. 15, 1981 to Hahn, to use two separate gas manifolds, each with its own inlet. Hahn permits the use of separate valves to control burners for cooking. In these burners the introduction of gas into each separate burner chamber has no effect on the distribution in any of the other burner chambers.
There is, therefore, a need for an improved burner and display apparatus for gas fireplaces and similar devices.